Development of corrosion resistant coatings is of commercial interest in, for example, the aerospace and automobile industries. In particular, the development of zinc (Zn) coatings has been an area of interest for protection of aerospace and automobile components made of steel. To further improve the corrosion resistance of zinc coatings, zinc alloys can be electrodeposited onto a steel substrate. For example, zinc-nickel (Zn—Ni) alloy has been used in the mass production of steel sheets for automobile bodies and also for small components such as nuts and bolts. Nonetheless, coatings having further improvement in corrosion resistance remain of interest.
Zinc-iron (Zn—Fe) alloy, for example, has excellent corrosion resistance, good weldability, paintability, and formability. In addition, zinc-iron alloy having high iron content serves as an effective undercoating for paints. Furthermore, the time for white rust formation of typical zinc-iron alloy coatings is often two to three times longer than that of a pure zinc metal coating.
Zinc-iron alloys can be deposited by electrodeposition. Electrodeposition of zinc-iron alloys often involves electrolyte solutions having a cyanide, an acid sulphate, ammonium chloride and/or an acid chloride. However, electrodeposition using these electrolyte solutions tends to deposit zinc metal onto a substrate under plating conditions in much larger quantities as compared to iron deposition. Commercially operated baths deposit less than 1% iron with zinc. This occurs because of formation of zinc hydroxide (Zn(OH)2) which inhibits the deposition of iron onto the substrate. Zn(OH)2 also adsorbs onto the cathode. Furthermore, complexing agents, such as ammonium chloride or amine based compounds complex very strongly with iron salts in the electrolyte solution which hinders iron metal deposition onto a substrate. Thus, formation of zinc alloys having high iron content is difficult to achieve and, accordingly, so are the beneficial properties of iron in a zinc iron alloy.
Therefore, there is a need in the art for improved electrolyte solutions for electrodeposition of zinc-iron alloys, methods of forming zinc-iron alloys, and methods of electrodepositing zinc-iron alloys.